An injection-locked PLL (phase lock loop) circuit is known as one type of PLL circuit. A voltage-controlled oscillator circuit of an injection-locked PLL circuit has a phase control function in addition to a frequency control function. A voltage-controlled oscillator circuit is supplied with a control voltage that has been generated by a charge pump and a loop filter based on a signal indicating a phase difference or frequency difference between a reference signal and a feedback signal. The frequency of an output signal of the voltage-controlled oscillator circuit is then controlled based on the control voltage. An injection signal based on a reference signal (for example, a clock signal of a predetermined frequency) is supplied to the voltage-controlled oscillator circuit, and phase control of the output signal is performed so as to be synchronized with the reference signal.
Note that when a delay circuit is used during generation of a pulse signal based on a reference signal as an injection signal, the pulse width becomes more easily affected by the power supply voltage, process fluctuations, and the like, making it difficult to achieve an optimum pulse width. For this reason, a technique that uses edges in a reference signal instead of the pulse signal as an injection signal has been proposed.
See, for example, the following documents:
Japanese Laid-open Patent Publication No. 07-95057;
Japanese Laid-open Patent Publication No. 2009-177297;
Japanese Patent No. 3,268,216;
Japanese Laid-open Patent Publication No. 2009-117894;
Japanese Laid-open Patent Publication No. 05-315899; and
W. Deng, D. Yang, A. Narayanan, K. Nakata, T. Siriburanon, K. Okada, and A. Matsuzawa, “A 0.048-mm2 3-mW Synthesizable Fractional-N PLL with a Soft Injection-Locking Technique”, IEEE International Solid-State Circuits Conference (ISSCC), 2015.
However, in a conventional injection-locked PLL circuit, when the output signal of the voltage-controlled oscillator circuit is injected before the frequency sufficiently converges, convergence of the frequency itself becomes difficult. This causes a need for processing, such as control for determining whether the frequency of the output signal has converged, as initialization processing in readiness for phase control, which makes phase control difficult.